Fuel-element containers of nuclear reactors are frequently supported in a metallic grid consisting of orthogonally intersecting bars, the containers being clamped between these bars (usually in an upright position) with the aid of a surrounding frame. In such reactors, which may be of the pressure-gas or the boiling-water type, very accurate tolerances must be observed as far as both the dimensions of the grid apertures and the parallelism and linearity of the bars is concerned. With grids measuring several meters in diameter, the weight of the structure may exert a distorting influence upon the bars. The assembly of such grids, moreover, is relatively laborious since precise mechanical interfitting of the parts is required and simpler techniques such as welding are excluded in view of the risk of thermal deformations.